An electric toothbrush internally equipped with a vibration source and configured to transmit the vibration from the vibration source to a brush portion is conventionally known. In such an electric toothbrush, the brush portion needs to be sufficiently vibrated to exhibit an effect of brushing teeth and to enable a user himself/herself to sufficiently have actual feeling of brushing teeth. If the vibration of the portion the user grips is too large when brushing teeth, the user sometimes feels unpleasant, and thus it is desirable that the relevant portion does not vibrate too much.
In order to sufficiently vibrate the brush portion and to not vibrate the portion the user grips with hand as much, consideration is made in arranging a vibration proof member for absorbing the vibration near the end on the opposite side of a component at which distal end the brush portion is arranged. However, this is not desirable in terms of energy efficiency since absorbing the vibration with the vibration proof member leads to losing some of the vibration energy generated by the vibration source.
Therefore, suppressing the vibration of the portion the user grips with hand while sufficiently vibrating the brush portion and suppressing the loss of vibration energy involve technical difficulty.
A technique of vibrating the brush portion by arranging an eccentric shaft bearing near the brush portion is known (Patent Document 3). However, such a technique has problems such as increase in slidable movement resistance and increase in an operation sound and vibration.
The related technique includes those disclosed in Patent Documents 1, 2, and 3.    [Patent Document 1] Japanese Examined Patent Publication No. 6-34796    [Patent Document 2] Japanese Unexamined Patent Publication No. 8-117258    [Patent Document 3] Japanese Unexamined Patent Publication No. 10-192054